First Evidence of Isoflavone Production by the Oomycete Aphanomyces euteiches , the Causal Agent of Legume Root Rot

Abstract

Aphanomyces euteiches is a destructive soilborne oomycete affecting legumes worldwide. Although its pathogenic mechanisms have been extensively investigated, its specialized metabolism remains largely unexplored. In this study, organic extracts of A. euteiches grown on two different media were tested across five legume species. The PDA-EtOAc extract induced the most severe yellowing and necrotic lesions on leaves, especially in pea and lentil, and markedly reduced root growth, with associated necrosis, in all legumes evaluated. GC-MS and 1H NMR profiling identified major fatty acids together with phenolic compounds and diketopiperazines potentially involved in microbial signaling. Daidzein and genistein, two plant isoflavones, were also identified in A. euteiches organic extracts for the first time. This finding challenges the current view that these metabolites detected during infection originate exclusively from legume hosts and suggests that they may also participate in pathogen biology and host–pathogen interactions.